Lost circulation additive, lost circulation treatment fluid made therefrom, and method of minimizing lost circulation in a subterranean formation

ABSTRACT

For lost circulation treatment for decreasing fluid loss from a borehole into a subterranean formation, a lost circulation additive including water soluble crosslinkable polymer, a crosslinking agent, a filter aid that is preferably diatomaceous earth, and optionally a reinforcing material. The method of forming a lost circulation fluid includes contacting the additive with water or an aqueous solution, with a method of lost circulation treatment of the formation further including the step of injecting the fluid into the formation thereby decreasing fluid loss from the borehole into the subterranean formation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to lost circulation additives andto methods of making such additives, to lost circulation treatmentfluids made therefrom and methods of making such fluids, to methods ofmodifying a well fluid using such additives and/or fluids, to methods ofoperating a well using such additives and/or fluids, and to methods ofminimizing lost circulation in a well using such additives and/orfluids. In another aspect, the present invention relates to lostcirculation additives comprising polymer, crosslinking agent, and filteraid and to methods of making such additives, to lost circulationtreatment fluids made therefrom and methods of making such fluids, tomethods of modifying a well fluid using such additives and/or fluids, tomethods of operating a well using such additives and/or fluids, and tomethods of minimizing lost circulation in a well using such additivesand/or fluids. In even another aspect, the present invention relates tolost circulation additives comprising a dry mixture of polymer,crosslinking agent, and filter aid and to methods of making suchadditives, to lost circulation treatment fluids made therefrom andmethods of making such fluids, to methods of modifying a well fluidusing such additives and/or fluids, and to methods of minimizing lostcirculation in a well using such additives and/or fluids. In stillanother aspect, the present invention relates to lost circulationadditives comprising polymer, crosslinking agent, and diatomaceous earth(“DE”), to lost circulation treatment fluids made therefrom, to methodsof minimizing lost circulation in a well using such fluids.

[0003] 2. Description of the Related Art

[0004] Subterranean wells are utilized to reach desirable oil and/or gasbearing formations, and are generally drilled utilizing rotary drillingtechniques. In such rotary drilling of wells for oil and gas, drillingfluids (“muds”) are circulated into the well through hollow tubulardrill pipe, past the teeth of the cutter head to sweep away the cuttingsfrom the cutter head, and returned to the surface along with thecuttings through the annulus surrounding the drill pipe. The drillingfluid is generally circulated in such a manner as to remove drillcuttings to prevent clogging of the cutter and to support the walls ofthe well hole. Such drill cuttings are entrained in the drilling fluidand brought to the surface with the fluid and then screened out anddiscarded. In addition to removing drill cuttings and supporting thewalls of the well hole, the drilling fluid also serves to cool andlubricate the drill bit and, in the case of systems employing downholedrill motors, it functions as a power fluid for the drill motor.

[0005] Typically, drilling fluids may be water-base, employing a base offresh water, salt water, or an oil-in-water emulsion in which waterforms the continuous phase, or oil-base, employing a relatively pure oilsuch as crude petroleum oil or diesel oil, or in may be an “invert”emulsion, a water-in-oil emulsion in which oil forms the continuousphase or a synthetic base employing a polymer.

[0006] Drilling fluids normally contain clays and/or other dispersedsolids which are employed to impart desired Theological properties tothe drilling fluid. Not only do these clays and/or other suspendedsolids impart desirable thixotropic properties to the drilling fluid,they also serve to coat the walls of the well with a relativelyimpermeable sheath, commonly termed a filter cake, which retards theflow of fluid from the well into the surrounding subterraneanformations.

[0007] In addition to clays and/or other suspended particles, a drillingfluid may also contain one or more weighting agents which function toincrease the density of the fluid to a level which will offset highpressures encountered during the drilling operation. Non-limitingexamples of suitable weighting agents which may be used in either waterbase or oil base drilling fluids include heavy minerals such as bariteand gelena.

[0008] One problem very commonly encountered during rotary drillingoperations is the problem of lost circulation in which part or all ofthe drilling fluid is not returned to the surface. This problem maymanifest itself anywhere from moderate losses of the drilling fluid, tosubstantial or even total losses of the drilling fluid such that littleor none of it is returned to the surface. Where a formation zone isidentified in which unacceptably large amounts of drilling fluid islost, such formation zone is commonly termed a “loss zone” or a losscirculation zone.” While there are many causes for loss circulation,non-limiting examples include those situations when the well encountersa formation of unusually high permeability or one which has naturallyoccurring horizontal or vertical fractures or fissures. Also, theformation may be fractured accidentally by the hydrostatic pressureexerted by the drilling mud, particularly when a change over to arelatively heavy mud is made in order to control high formationpressures.

[0009] As can be expected, over the years numerous techniques have beendeveloped to prevent or reduce loss circulation. One common techniquewhere the loss circulation is not so severe is to add various fluid lossagents which function to change the rheological properties of thedrilling mud in order to increase its resistence to flow from the wellbore into the formation. Such fluid loss agents include syntheticpolymeric thickening agents such as partially hydrolyzed polyacrylamide,polyelectrolite such as an ionic polysaccharide, various gums such aslocust bean gum and guar gum, various starches, andcarboxymethylcellulose (CMC) or carboxyethylcellulose (CEC).

[0010] Where the loss circulation is more severe, it is a normalpractice to incorporate into the drilling mud various bulk materialswhich function to combat or prevent loss circulation. It has been commonin the past to add any number of materials to the drilling fluid whichact to reduce or prevent flow of the drilling fluid from the well holeto the formation. These materials are commonly referred to as “loss (orlost) circulation additives”. Such prior art loss circulation materialsinclude fibrous, flake (or laminated), and granular materials. Anonexhaustive list of such loss circulation includes nut and seed shellsor hulls (peanut almond, walnut, peach, brazil, coconut, peanut,sunflower, flax, cocoa bean, cottonseed, rice, linseed) ; crude pectatepulp; feathers; citrus pulp; beet pulp; peat moss fibers; jute; flax;mohair; lechuguilla fibers; cotton; cotton linters; wool; paper;wet-strength paper; sugar cane; bagasse; bamboo; corn stalks; sawdust;straw; wood fiber; cedar fiber; bark chips; cork; popped popcorn;dehydrated vegetable matter (suitably dehydrated carbohydrates such ascitrus pulp, oatmeal, tapioca, rice grains, potatoes, carrots, beets,and various grain sorghams); the ground woody ring portion of corn cobs;whole ground corn cobs; hydrophobic, organophilic, water-wettablefibrous materials such as treated cotton, dried bagasse, and dried peatfibers; and specific mixtures of these materials. Many assortedinorganic materials have also been utilized as loss circulationmaterials.

[0011] Seepage losses can occur to any type of loss zone and in any typeof formation when the particles in the drilling fluid are not fineenough to complete the seal. It has been established that the maximumallowable drilling fluid loss is on the order of 1 bbl/hr (0.16m³/h), asmeasured in the mud pit at the surface.

[0012] There are numerous examples of patents teaching the use ofvarious types of materials for use as lost circulation additives indrill fluids. The following are not an exhaustive sampling.

[0013] U.S. Pat. No. 2,610,149, issued Sep. 9, 1952, to Van Dyke,discloses the use of corn stalks, wood shavings, flake cellophane andchopped up paper in drilling fluids.

[0014] U.S. Pat. No. 2,779,417, issued Jan. 29, 1957, to Clark et al.,discloses the use of cellophane, rice hulls and shredded paper asbridging agents in a well fluid.

[0015] U.S. Pat. No. 4,247,403, issued Jan. 27, 1981, to Foley et al.,discloses the use of whole corncobs or the woody ring portion ofcorncobs as loss circulation additives for drilling fluids.

[0016] U.S. Pat. No. 4,474,665, issued Oct. 2, 1984 to Green, disclosesa lost circulation material useful in drilling fluids formed from cocoabean shell material having a particle size distribution from 2 to 100mesh.

[0017] U.S. Pat. No. 4,579,668, issued Apr. 1, 1986 to Messenger,discloses for use as drilling fluid bridging agents, ground walnutshells, cellophane and shredded wood.

[0018] U.S. Pat. No. 5,004,553, issued Apr. 2, 1991, and U.S. Pat. No.5,071,575, issued Dec. 10, 1991, both to House et al., disclose a wellworking composition containing oat hulls and optionally including one ormore of ground corn cobs, cotton, citrus pulp, and ground cotton burrs.

[0019] U.S. Pat. No. 5,076,944, issued Dec. 31, 1991 to Cowan et al.,discloses a seepage loss additive comprising ground cotton burrs incombination with one or more of ground oat hulls, ground corn cobs,cotton, ground citrus pulp, ground peanut shells, ground rice hulls, andground nut shells.

[0020] U.S. Pat. No. 5,118,664, issued Jun. 2, 1992, and U.S. Pat. No.5,599,776, issued Feb. 4, 1997, both to Burts, Jr., disclose the use ofvarious comminuted plant materials as lost circulation materials.

[0021] U.S. Pat. No. 4,957,166, issued Sep. 18, 1990 to Sydansk,discloses the use of a water soluble carboxylate crosslinking polymeralong with a chromic carboxylate complex crosslinking agent as a lostcirculation material. Sydansk further teaches that the performancerequirements of conformance improvement treatment polymers are differentfrom those of lost circulation polymers. Thus, while U.S. Pat. No.5,377,760, issued Jan. 3, 1995 to Merrill discloses addition of fibersto an aqueous solution of partially hydrolyzed polyacrylamide polymer,with subsequent injection into the subterranean to improve conformance,Sydansk teaches that such would not necessarily work for lostcirculation treatment.

[0022] Additionally, Merrill's conformance treatment method of mixingthe fibers with the polymer solution followed by injection, requires amultiplicity of storage and mixing tanks, and a metering system whichmust be operated during the operation of the well. Specifically, a firsttank will store a water and polymer solution, a second tank will store awater and cross-linking solution, and a third tank will be used to mixfibers with polymer solution from the first tank to create apolymer/fiber slurry. This polymer/fiber slurry is then metered from thethird tank and combined with cross-linking solution metered from thesecond tank to the well bore.

[0023] As an advance over the above prior art, U.S. Pat. No. 6,016,879,issued Jan. 25, 2000, to Boyce D. Burts, Jr., for “Lost circulationadditive, lost circulation treatment fluid made therefrom, and method ofminimizing lost circulation in a subterranean formation,” discloses anadditive including a “dry mixture” of water soluble crosslinkablepolymer, a crosslinking agent, and a reinforcing material of fibersand/or comminuted plant materials. The method of forming a fluidincludes contacting the additive with water or an aqueous solution, witha method of treating the formation further including the step ofinjecting the fluid into the formation.

[0024] While not believed to be related prior art because they relate todifferent types of well operations, for completeness, attention isdirected to five other similar “dry mixture” patents by Boyce D. Burts,Jr., which were filed on the same day (Oct. 31, 1997) as the '879Patent: U.S. Pat. No. 6,218,343, issued Apr. 17, 2001, for “Additivefor, treatment fluid for, and method of plugging a tubing/casing annulusin a well bore,” U.S. Pat. No. 6,102,121, issued Aug. 15, 2000, for“Conformance improvement additive, conformance treatment fluid madetherefrom, method of improving conformance in a subterranean formation,”U.S. Pat. No. 6,098,712, issued Aug. 8, 2000, for “Method of plugging awell,” U.S. Pat. No. 6,016,871, issued Jan. 25, 2000, for “Hydraulicfracturing additive, hydraulic fracturing treatment fluid madetherefrom, and method of hydraulically fracturing a subterraneanformation,” and U.S. Pat. No. 6,016,869, issued Jan. 25, 2000, for “Wellkill additive, well kill treatment fluid made therefrom, and method ofkilling a well.”

[0025] A number of patents discuss the use of diatomaceous earth (“DE”)in a well operation.

[0026] U.S. Pat. No. 3,380,542, issued Apr. 30, 1968 to Clear, forrestoring lost circulation discloses a oil-based drilling fluid,containing a slurry of diatomite and asbestos, used to restore lostcirculation during well drilling operations.

[0027] U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, disclosesthat various formation sealing agents have been used in the art to formformation seals and/or filter cakes on the wall of a well bore,including diatomaceous earth.

[0028] U.S. Pat. No. 4,110,225, issued Aug. 29, 1978 to Cagle, disclosesthat zones of lost circulation and other undesired fluid communicationchannels into a wellbore are sealed by isolating a volume in the wellincluding such a zone and applying greater than formation pressure to anovel slurry spotted in the zone until it hardens into a solid,drillable seal. The slurry contains per barrel from 5-50 poundsdiatomaceous mix, from about 35 to about 350 pounds of oil well cement,and at a minimum about 5 to 6 pounds of a flake type lost-circulationagent. This '225 patent cites a number of patents that disclosecement/diatomaceous earth compositions, including U.S. Pat. Nos.2,585,336; 2,793,957; 2,961,044; 3,467,198; and 3,558,335.

[0029] Regarding these patents, the '225 patent notes the following:

[0030] Regarding U.S. Pat. No. 2,585,336, the '225 patent notes, “amixture is made using from 2% to 100% diatomaceous earth, compared tothe content of the cement in the slurry. The aim of the inventors was toprevent perlite from settling and to produce a lightweight cement. Thediatomaceous earth-cement described in the disclosure is a mixture ofPortland cement, perlite and diatomaceous earth, lime, and asbestosfibers.”

[0031] Regarding U.S. Pat. No. 2,793,957, the '225 patent notes, “refersto a highly permeable cement formed by use of the same basic mixtures ofdiatomaceous earth with Portland cement, the diatomaceous earth presentbeing from five to seven times the proportion of the Portland cement inthe slurry. The aim of the inventors was to produce a light highlypermeable cement, entirely opposite to the purpose of my invention.”

[0032] Regarding U.S. Pat. No. 2,961,044, the '225 patent notes,“discusses and claims a cement composition which has diatomaceous earthin the amounts of from 30% to 70% of the Portland cement. The reason forusing the diatomaceous earth was to prevent the strength retrogressionof a salt-saturated cement. Thus, while Shell wishes (among other uses)to employ his mixture for squeeze cementing, he produces a relativelyhigh-strength cement plug. There is a real tendency when redrilling sucha plug for the bit to be deflected or sidetracked so that the new holeis beside rather than through the bore and the seal is ineffective. Thisis completely different from my invention which minimizes such tendencyby producing a plug at least as drillable as the formation in which itis set. Also, Shell is directed to operations using salt-saturatedcement slurries, while I prefer using a fresh or brackish water slurry.I employ lost-circulation agents; he makes no teaching of using suchadditives. Accordingly, his teaching is quite far from mine.”

[0033] Regarding both U.S. Pat. Nos. 3,467,198 and 3,558,335, the '225patent notes, “describe cement compositions having diatomaceous mixpresent in the amounts from 0.5% to 10% of the amount of Portland cementpresent to prevent solids-settling.”

[0034] U.S. Pat. No. 4,369,844, issued Jan. 25, 1983 to Clear, disclosesslurries to seal permeable earth formations encountered in the drillingof wells, comprising finely divided paper, diatomaceous earth, and in afurther embodiment, lime. A slug of the slurry is spotted at the locusof the permeable formation and defluidized to form a formation seal onwhich a mud sheath is then deposited.

[0035] U.S. Pat. No. 4,505,751, issued Mar. 19, 1985, discloses asilicate/silica cement in oil field applications, including diatomaceousearth as a species of silica compound.

[0036] While not believed to be analogous prior art because it relatesto earthen pits (for example a ditch) and not to subterrean wellboresnor well operations, U.S. Pat. No. 5,947,644, issued Sep. 7, 1999 toGibbons et al., is included herein for completeness because it disclosesa gelable slurry of aqueous solvent, a crosslinkable polymer, acrosslinking agent, and unconsolidated solids such as diatomaceousearth. This gelable slurry is placed in an earthen pit and allowed toform into a fluid impermeable barrier wall in the earthen pit. Thepolymer serves to bind the unconsolidated solids to convert the gelableslurry to a nondeformable gelled continuum of consolidated solids, whichforms the barrier wall in the earthen pit. As disclosed in the '644Patent in the Summary of the Invention section, at col. 1, lines 57-67,this gelable slurry is prepared by first forming a liquid gelationsolution of the polymer and crosslinking agent, to which is subsequentlymixed with the unconsolidated solids, or alternatively, by sequentiallymixing the aqueous solvent, crosslinkable polymer, and polymercrosslinking agent with the unconsolidated solids.

[0037] Thus, in spite of the advancements in the prior art, there stillneed for further innovation in the lost circulation art.

[0038] There is need for further innovation for lost circulation artutilizing a water soluble polymer.

[0039] There is another need for lost circulation technology which wouldallow for simplification of the mixing equipment.

[0040] These and other needs in the art will become apparent to those ofskill in the art upon review of this specification, including itsdrawings and claims.

SUMMARY OF THE INVENTION

[0041] It is an object of the present invention to provide for furtherinnovation in the lost circulation art.

[0042] It is an another object of the present invention to provide forfurther innovation for lost circulation art utilizing a water solublepolymer.

[0043] It is even another object of the present invention to provide forlost circulation art which would allow for simplification of the mixingequipment.

[0044] These and other objects of the present invention will becomeapparent to those of skill in the art upon review of this specification,including its drawings and claims.

[0045] According to one embodiment of the present invention, there isprovided a lost circulation additive comprising a water solublecrosslinkable polymer, a crosslinking agent, and a filter aid. In afurther embodiment of this embodiment, the additive is a dry mixture.

[0046] According to another embodiment of the present invention, thereis provided a well fluid comprising a lost circulation fluid, watersoluble crosslinkable polymer, a crosslinking agent, and a filter aid.

[0047] According to even another embodiment of the present invention,there is provided a method of modifying a lost circulation fluid. Themethod generally includes providing a lost circulation additivecomprising a mixture of water soluble crosslinkable polymer, acrosslinking agent, and a filter aid. While this additive may be in anyform, it is preferably a dry mixture. The method also includescontacting the lost circulation fluid with the lost circulation additiveto form a modified lost circulation fluid.

[0048] According to still another embodiment of the present invention,there is provided a method for plugging an opening in a subterraneanformation. The method includes providing a lost circulation fluidcomprising water or an aqueous solution, water soluble crosslinkablepolymer, a crosslinking agent, and a filter aid. The method alsoincludes injecting the lost circulation fluid into the formation andinto the opening to be plugged. The method also includes dewatering thelost circulation fluid to force the polymer and crosslinking agentthrough the opening and into the formation, and to form the filter aidinto a plug in the opening.

[0049] According to yet another embodiment of the present invention,there is provided a method for plugging an opening in a subterraneanformation. The method includes providing a lost circulation fluidcomprising water or an aqueous solution, water soluble crosslinkablepolymer, a crosslinking agent, and a filter aid. The method alsoincludes injecting the lost circulation fluid into the formation andinto the opening to be plugged. The method also includes applyingpressure to dewater the lost circulation fluid to force the polymer andcrosslinking agent through the opening and into the formation, and toform the filter aid into a plug in the opening.

[0050] According to even yet another embodiment of the presentinvention, there is provided a method of circulating a fluid in awelbore penetrating a subterranean formation. The method includesproviding a lost circulation fluid comprising water or an aqueoussolution, water soluble crosslinkable polymer, a crosslinking agent, anda filter aid. The method also includes circulating the lost circulationfluid in the wellbore.

[0051] According to even yet another embodiment of the presentinvention, there is provided a method of modifying a lost circulationfluid circulating in a wellbore penetrating a subterranean formation.The method includes introducing a water soluble crosslinkable polymer,crosslinking agent, and filter aid to the circulating lost circulationfluid.

[0052] Various further embodiments of any or all of the aboveembodiments include any or all of the following in any combination: thefilter aid is selected from the group consisting of diatomaceous earth,perlite, glass beads, magnesium silicate, solid thermoplastic orthermoset polymer beads, talc, and calcium silicate; or the polymer isan a carboxylate-containing polymer, and the crosslinking agent isselected from the group consisting of chromium (III) carboxylatecomplexes, aldehydes, dialdehydes, formaldehydes, glutaraldehyde,dichromates, titanium chelates, phenols, substituted phenols, ethers,aluminum citrate, and aluminates; the filter aid comprises at least oneof diatomaceous earth or pearlite; the polymer comprises a low molecularweight polymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000;the polymer is a water soluble, carboxylate containing acrylamide, andthe crosslinking agent is a chromium (III) carboxylate complex; thefilter aid is diatomaceous earth; the filter aid is pearlite; thereinforcing material selected from the group consisting of hydrophilicfibers, hydrophobic fibers, and comminuted plant material; and/orvarious weight percentages are in the range of about 4 to about 35weight percent polymer, in the range of about 1 to about 10 weightpercent cross linking agent, and in the range of about 55 to about 95weight percent filter aid, based on the total weight of the polymer,cross linking agent and filter aid.

[0053] These and other embodiments of the present invention will becomeapparent to those of skill in the art upon review of this specificationand claims.

DETAILED DESCRIPTION OF THE INVENTION

[0054] The lost circulation additive of the present invention includespolymer, cross-linking agent, filter aid, and optionally a reinforcingmaterial, preferably either fibers or comminuted particles of plantmaterials, and optionally any other materials that are known in the art.It is to be understood that the lost circulation additive of the presentinvention may be in the form of a dry mixture or a slurry. In apreferred embodiment of the present invention, the lost circulationadditive is a dry mixture.

[0055] A well fluid of the present invention comprises the additive ofthe invention. In a method of modifying a lost circulation fluid to forma modified lost circulation fluid, the lost circulation fluid to bemodified is contacted the additive or well fluid of the presentinvention.

[0056] Any suitable relative amounts of the polymer, cross-linkingagent, filter aid and the optional reinforcing materials may be utilizedin the present invention provided that the desired lost circulationresults are achieved. Generally, the relative amounts of each will bedetermined based on the particular application to which the additive isto be subjected. A suitable amount of crosslinking agent is provided toreach the desired amount of crosslinking. The amount of optionalreinforcing material is selected to provide desired physical properties.

[0057] Any suitable types of filter aid materials as are known in thefiltration art may be utilized as the filter aid component in thepresent invention. All that is necessary is that the filter aid willfunction to be “squeezed” and allow migration of the solution of polymerand crosslinking agent into the formation, and will form a plug of thefilter aid that will hold the solution in place until it sufficientlycrosslinks. Non-limiting examples of which include diatomaceous earth(“DE” or diatomite), perlite (or pearlite), glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymers generally in powderform, talc (naturally occuring form of hydrous magnesium silicatecontaining varying proportions of such associated minerals asalpha-quartz, calcite, chlorite, dolomite, kaolin, magnesite, andphlogopite), and calcium silicate (for example, see, U.S. Pat. No.5,750,038, issued May 12, 1998, to Tsunematsu, for “Method for thepreparation of acid-resistant calcium silicate,” incorporate herein byreference), and any combination of two or more of the above. Preferably,the filter aid is selected from the group consisting of diatomaceousearth perlite (or pearlite), magnesium silicate, and talc. Morepreferably, the filter aid is a mineral based type of filter aid,non-limiting examples of which include diatomaceous earth, pearlite,magnesium silicate, talc and calcium silicate, and any combination oftwo or more of the above. Even more preferably, the filter aid comprisespearlite and/or diatomaceous earth. Still more preferably, the filteraid comprises diatomaceous earth.

[0058] The amount of filter aid to be utilized is generally notdependent upon the amount of polymer or crosslinking agent, but rather,is that amount sufficient to form a plug to retain the polymer in placeuntil it crosslinks sufficiently to remain in place on its own. However,in an effort to quantify the amount of filter aid, a weight ratio offilter aid to polymer is provided for convenience.

[0059] Generally, the weight ratio of filter aid:polymer in the additiveis in the range of about 100:1 to about 1:100, preferably in the rangeof about 50:1 to about 1:50, more preferably in the range of about 15:1to about 1:15, even more preferably in the range of about 5:1 to about1:5, and still more preferably in the range of about 5:1 to about 1:1.

[0060] Commercially, it is envisioned that the additive will be packagedin a single bag, to promote ease of use and eliminate the necessity ofany measuring and/or mixing at the well site. As a non-limiting exampleof a commercial embodiment, a 40 pound bag might contain any where fromabout 1.5 to about 17.5 lbs. polymer, from about 0.4 to about 5 lbs.crosslinking agent, and the balance of from about 17.5 to about 38.1lbs. filter aid.

[0061] In weight percentage terms, examples of weight percentage rangesinclude from about 4 to about 35 weight percent polymer, from about 1 toabout 10 weight percent cross linking agent, and from about 55 to about95 weight percent filter aid, based on the total weight of the polymer,cross linking agent and filter aid. Specific non-limiting examples ofuseful compositions include 4% polymer, 1% cross linker, 95% DE, or 24%polymer, 6% cross linker, 70% DE, or 35% polymer, 10% cross linker, 55%DE.

[0062] The particle size distribution of the filter aid is selected toallow dewatering of the filter aid (i.e., the solution containingpolymer and crosslinking agent will separate from the filter aid), andto allow formation of a plug of the filter aid that retains the polymerand crosslinking agent in the reservoir during crosslinking. It isbelieved that the particle size distribution will be determined by thereservoir conditions.

[0063] Other additives as are known in the well fluid art may beutilized, non limiting examples of which include surfactants,dispersants, retarders, accelerants, weighting agents (such as hematite,barite or calcium carbonate), lost circulation materials and otheradditives may be provided as necessary or desired.

[0064] The polymer utilized in the practice of the present invention ispreferably water soluble and must be capable of being pumped as a liquidand subsequently crosslinked in place to form a substantiallynon-flowing crosslinked polymer which has sufficient strength towithstand the pressures exerted on it. Optionally, when reinforcingmaterials are utilized, it would have a network structure capable ofincorporating reinforcing materials.

[0065] While any suitable water soluble polymer may be utilized, thepreferred polymer utilized in the practice of the present invention is awater soluble carboxylate-containing polymer, more preferably a watersoluble partially hydrolyzed carboxylate-containing polymer. Thiscarboxylate-containing polymer may be any crosslinkable, high molecularweight, water-soluble, synthetic polymer or biopolymer containing one ormore carboxylate species.

[0066] For an example of polymers and crosslinking agents suitable foruse herein and details regarding their making and use, please see any ofthe above listed patents to Boyce D. Burts, Jr. all herein incorporatedby reference, or please see U.S. Pat. Nos. 4,683,949, 4,723,605,4,744,418, 4,770,245, 4,844,168, 4,947,935, 4,957,166 and 4,989,673,5,377,760, 5,415,229, 5,421,411, all herein incorporated by reference.

[0067] The average molecular weight of the carboxylate-containingpolymer utilized in the practice of the present invention is in therange of about 10,000 to about 50,000,000, preferably in the range ofabout 100,000 to about 20,000,000, more preferably in the range of about200,000 to about 15,000,000, and still more preferably in the range ofabout 200,000 to about 10,000,000.

[0068] In some instances, a blend of two polymers, a lower molecularweight polymer and a higher molecular weight polymer may be utilized.For example, in some instances where high fluid loss is encountered,such as a hole in the casing, a fault zone, loose sand, unconsolidatedzones, or vugular formations, higher molecular weight polymer must beutilized. However, this higher molecular weight polymer causes problemsin mixing, pumping and total polymer load. Thus, this higher molecularweight polymer is mixed with a lower molecular weight polymer to providemixing, pumping and loading as desired.

[0069] Generally, this lower molecular weight polymer has a molecularweight less than 1,000,000, preferably less than 500,000, and morepreferably less than 200,000. Generally the lower molecular weightpolymer will have a molecular weight in the range of about 20,000 toless than 1,000,000, preferably in the range of about 20,000 to lessthan 500,000, and more preferably in the range of about 200,000 to lessthan 500,000. The higher molecular weight polymer generally has amolecular weight of at least 1,000,000, preferably from about 1,000,000to about 50,000,000, more preferably from about 5,000,000 to about20,000,000, and even more preferably from about 6,000,000 to about12,000,000.

[0070] Biopolymers useful in the present invention includepolysaccharides and modified polysaccharides. Non-limiting examples ofbiopolymers are xanthan gum, guar gum, carboxymethylcellulose,o-carboxychitosans, hydroxyethylcellulose, hydroxypropylcellulose, andmodified starches. Non-limiting examples of useful synthetic polymersinclude acrylamide polymers, such as polyacrylamide, partiallyhydrolyzed polyacrylamide and terpolymers containing acrylamide,acrylate, and a third species. As defined herein, polyacrylamide (PA) isan acrylamide polymer having substantially less than 1% of theacrylamide groups in the form of carboxylate groups. Partiallyhydrolyzed polyacrylamide (PHPA) is an acrylamide polymer having atleast 1%, but not 100%, of the acrylamide groups in the form ofcarboxylate groups. The acrylamide polymer may be prepared according toany conventional method known in the art, but preferably has thespecific properties of acrylamide polymer prepared according to themethod disclosed by U.S. Pat. No. Re. 32,114 to Argabright et alincorporated herein by reference.

[0071] Any crosslinking agent suitable for use with the selected polymermay be utilized in the practice of the present invention. Non limitingexamples of suitable crosslinking agents includes chromium (III)carboxylate complexes, aldehydes, dialdehydes, formaldehydes,glutaraldehyde, dichromates, titanium chelates, phenols, substitutedphenols, ethers, aluminum citrate, and is aluminates.

[0072] Preferably, the crosslinking agent utilized in the presentinvention is a chromic carboxylate complex.

[0073] The term “complex” is defined herein as an ion or moleculecontaining two or more interassociated ionic, radical or molecularspecies. A complex ion as a whole has a distinct electrical charge whilea complex molecule is electrically neutral. The term “chromiccarboxylate complex” encompasses a single complex, mixtures of complexescontaining the same carboxylate species, and mixtures of complexescontaining differing carboxylate species.

[0074] The chromic carboxylate complex useful in the practice of thepresent invention includes at least one or more electropositive chromiumIII species and one or more electronegative carboxylate species. Thecomplex may advantageously also contain one or more electronegativehydroxide and/or oxygen species. It is believed that, when two or morechromium III species are present in the complex, the oxygen or hydroxidespecies may help to bridge the chromium III species. Each complexoptionally contains additional species which are not essential to thepolymer crosslinking function of the complex. For example, inorganicmono- and/or divalent ions, which function merely to balance theelectrical charge of the complex, or one or more water molecules may beassociated with each complex. Non-limiting representative formulae ofsuch complexes include:

[Cr₃(CH₃CO₂)₆(OH)₂]¹⁺;

[Cr₃(CH₃CO₂)₆(OH)₂]NO₃·6H₂O;

[Cr₃ (CH₃CO₂)₆(OH)₂]³⁺; and

[Cr₃ (CH₃CO₂)₆(OH)₂](CH₃CO₂)₃·H₂O.

[0075] “Trivalent chromium” and “chromic ion” are equivalent termsencompassed by the term “chromium III” species as used herein.

[0076] The carboxylate species are advantageously derived fromwater-soluble salts of carboxylic acids, especially low molecular weightmono-basic acids. Carboxylate species derived from salts of formic,acetic, propionic, and lactic acid, substituted derivatives thereof andmixtures thereof are preferred. The preferred carboxylate speciesinclude the following water-soluble species: formate, acetate,propionate, lactate, substituted derivatives thereof, and mixturesthereof. Acetate is the most preferred carboxylate species. Examples ofoptional inorganic ions include sodium, sulfate, nitrate and chlorideions.

[0077] A host of complexes of the type described above and their methodof preparation are well known in the leather tanning art. Thesecomplexes are described in Shuttleworth and Russel, Journal of theSociety of Leather Trades' Chemists, “The Kinetics of Chrome TannagePart I.,” United Kingdom, 1965, v. 49, p. 133-154; “Part III.,” UnitedKingdom, 1965, v. 49, p. 251-260; “Part IV.,” United Kingdom, 1965, v.49, p. 261-268; and Von Erdman, Das Leder, “Condensation of MononuclearChromium (III) Salts to Polynuclear Compounds,” Eduard Roether Verlag,Darmstadt Germany, 1963, v. 14, p. 249; and incorporated herein byreference. Udy, Marvin J., Chromium. Volume 1: Chemistry of Chromium andits Compounds. Reinhold Publishing Corp., New York, 1956, pp. 229-233;and Cotton and Wilkinson, Advanced Inorganic Chemistry 3rd Ed., JohnWiley and Sons, Inc., New York, 1972, pp. 836-839, further describetypical complexes which may be within the scope of the present inventionand are incorporated herein by reference. The present invention is notlimited to the specific complexes and mixtures thereof described in thereferences, but may include others satisfying the above-stateddefinition.

[0078] Salts of chromium and an inorganic monovalent anion, e.g., CrCl3,may also be combined with the crosslinking agent complex to accelerategelation of the polymer solution, as described in U.S. Pat. No.4,723,605 to Sydansk, which is incorporated herein by reference.

[0079] The molar ratio of carboxylate species to chromium III in thechromic carboxylate complexes used in the process of the presentinvention is typically in the range of 1:1 to 3.9:1. The preferred ratiois range of 2:1 to 3.9:1 and the most preferred ratio is 2.5:1 to 3.5:1.

[0080] The optional reinforcing material of the present invention maycomprise fibers or comminuted particles of plant materials, andpreferably comprises comminuted particles of one or more plantmaterials.

[0081] Fibers suitable for use in the present invention are selectedfrom among hydrophilic and hydrophobic fibers. Incorporation ofhydrophobic fibers will require use of a suitable wetting agent.Preferably, the fibers utilized in the present invention comprisehydrophilic fibers, most preferably both hydrophilic and hydrophobicfibers.

[0082] With respect to any particular fiber employed in the practice ofthe present invention, it is believed that the longer the fiber, themore difficult it is to be mixed uniformly in solution. It is believedthat fibers as long as 12,500 microns may tend to aggregate and formclumps. The shorter the fiber, it is believed the easier it is to mix insolution. On the other hand, the shorter the fiber, the greater thequantity necessary to provide the desired level of strength in areinforced mature gel. In general, the fibers utilized in the presentinvention will have a length in the range of 100 microns to 3200microns, preferable 100 microns to 1000 microns.

[0083] Non-limiting examples of suitable hydrophobic fibers includenylon, rayon, hydrocarbon fibers and mixtures thereof.

[0084] Non-limiting examples of suitable hydrophilic fibers includeglass, cellulose, carbon, silicon, graphite, calcined petroleum coke,cotton fibers, and mixtures thereof.

[0085] Non-limiting examples of comminuted particles of plant materialssuitable for use in the present invention include any derived from: nutand seed shells or hulls such as those of peanut, almond, brazil, cocoabean, coconut, cotton, flax, grass, linseed, maize, millet, oat, peach,peanut, rice, rye, soybean, sunflower, walnut, wheat; various portionsof rice including the rice tips, rice straw and rice bran; crude pectatepulp; peat moss fibers; flax; cotton; cotton linters; wool; sugar cane;paper; bagasse; bamboo; corn stalks; various tree portions includingsawdust, wood or bark; straw; cork; dehydrated vegetable matter(suitably dehydrated carbonhydrates such as citrus pulp, oatmeal,tapioca, rice grains, potatoes, carrots, beets, and various grainsorghams); whole ground corn cobs; or various plant portions the corncob light density pith core, the corn cob ground woody ring portion, thecorn cob coarse or fine chaff portion, cotton seed stems, flax stems,wheat stems, sunflower seed stems, soybean stems, maize stems, rye grassstems, millet stems, and various mixtures of these materials.

[0086] Optionally a dispersant for the comminuted plant material in therange of about 1 to about 20 pounds, preferably in the range of about 5to about 10 pounds, and more preferably in the range of about 7 to about8 pounds of dispersant may be utilized per pound of comminuted plantmaterial. A non-limiting example of a dispersant would be NaCl.

[0087] Preferred comminuted materials useful in the practice of thepresent invention include those derived from peanuts, wood, paper anyportion of rice seed or plant, and any portion of corn cobs.

[0088] These various materials can be comminuted to very fine particlesizes by drying the products and using hammer mills, cutter heads, aircontrol mills or other comminution methods as is well known to those ofskill in the comminution art. Air classification equipment or othermeans can be used for separation of desired ranges of particle sizesusing techniques well-known in the comminution art.

[0089] Any suitable size of comminuted material may be utilized in thepresent invention, along as such size produces results which aredesired. Of course, the particle size will be a function of diameter ofthe porosity passages. While the present invention will find utility forpassages on the order of microns in diameter, it will also find utilityon larger passages, for example, those with diameters greater than{fraction (1/64)}, {fraction (1/16)} or event ⅛ of an inch.

[0090] In most instances, the size range of the comminuted materialsutilized herein will range from below about 8 mesh (“mesh” as usedherein refers to standard U.S. mesh), preferably from about −65 mesh toabout −100 mesh, and more preferably from about −65 mesh to about −85mesh. Specifically preferred particle sizes for some materials areprovided below.

[0091] Preferred mixtures of comminuted materials useful in the practiceof the present invention include a rice fraction and peanut hulls; arice fraction and wood fiber and/or almond hulls; a rice fraction and acorn cob fraction, preferably a chaff portion; and a corn cob fraction,preferably a pith or chaff portion, a rice fraction, and at least one ofwood fiber, nut shells, paper and shredded cellophane.

[0092] Rice is commercially available in the form of rice hulls, ricetips, rice straw and rice bran, as these various parts of the rice plantare separated commercially and are widely available from rice mills.Preferably, the size range of the rice fraction utilized herein willrange from below about 8 mesh (“mesh” as used herein refers to standardU.S. mesh), preferably from about −65 mesh to about −100 mesh, and morepreferably from about −65 mesh to about −85 mesh.

[0093] After the corn kernals are removed, corn cobs consist of fourprinciple parts that are arranged concentrically. The central portion isa very light density pith core, that is surrounded by a woody ring, thatin turn is surrounded by a coarse chaff portion, that in turn is coveredby a fine chaff portion. The coarse and fine chaff portions form thesockets for ancoring the corn kernels to the corncob. The normal methodsof grinding corncobs produce a mixture of all four parts enumeratedabove. It is possible, however, to separate the woody ring material fromthe remainder of the cob. The chaff portion of the corncob remainingafter removal of the woody ring material is known as “bees wings”. Inthe present invention, any of the pith or chaff portions (“BPC”) are thepreferred portions of the corn cob, with the chaff portions being morepreferred. A range of particle sizes of pith and chaff can be obtainedfrom comminution, but the size range smaller than about 8 mesh issuitable for this invention. Preferably, a particle size distributionranging from smaller than 8 mesh to smaller than 100 mesh is utilized.

[0094] Preferred woods for use as comminuted materials in the presentinvention include any type of hard wood fiber, including cedar fiber,oak fiber, pecan fiber and elm fiber. Preferably the wood fibercomprises cedar fibers.

[0095] Preferred nut shells for use in the present invention includepecan, walnut, and almond. Preferably, the nut shells comprise at leastone of pecan or walnut shells.

[0096] Preferred particle sizes for the wood fibers, nut shells, paperand cellophane will generally range from about +10 mesh to −100 mesh. Anillustration of a non-limiting particle size distribution for thesematerials would include particles of +10 mesh, +20 mesh, +30 mesh, +50mesh, +60 mesh, +100 mesh, and −100 mesh.

[0097] For one of the preferred comminuted plant mixtures comprising acorn cob fraction, a rice fraction, and at least one of wood fiber, nutshells, paper and shredded cellophane, the mixture will generallycomprise in the range of about 5 to about 95 weight percent rice, in therange of about 5 to about 95 weight percent corncob pith or chaff, withthe total of ground wood fiber, ground nut shells, ground paper andshredded cellophane comprising in the range of about 5 to about 95weight percent (weight percent based on the total weight of plantmaterial in the mixture. Preferred ranges are about 20 to about 75weight percent rice, about 5 to about 35 weight percent corncob pith orchaff, with the total of ground wood fiber, ground nut shells, groundpaper and shredded cellophane comprising in the range of about 20 toabout 75 weight percent. More preferred ranges are about 30 to about 50weight percent rice, about 10 to about 30 weight percent corncob pithand chaff, with the total of ground wood fiber, ground nut shells,ground paper and shredded cellophane comprising in the range of about 25to about 50 weight percent.

[0098] As these comminuted materials are to be added to a water baselost circulation fluid, a small amount of oil may optionally added tothe mixture. This optional oil is preferably added while the plantmaterials are being mixed together. This mixing may take place in aribbon blender, where the oil in the required amount is applied by aspray bar. The oil wets the particles and adds to their lubricity whileat the same time helping to control dust produced by the mixingoperation. A variety of oils may be utilized in the practice of thepresent invention in concentrations generally ranging from about 1percent to about 5 percent by weight based on the total weight of themixture of comminuted materials, more preferably ranging from about 1percent to about 2 percent. A non-limiting example of a commerciallyavailable oil suitable for use in the present invention includes ISOPARV, available from Exxon Corporation.

[0099] In the method of the present invention for forming a lostcirculation additive, the various components of polymer, crosslinkingagent and filter aid, may be mixed in any form (dry form, liquid form,or slurry form) in any suitable order utilizing mixing techniques asknown to those in the art.

[0100] Specifically, a dry lost circulation additive may be formed bymixing solid polymer, solid crosslinking agent and solid filter aid toform a solid (dry) lost circulation additive.

[0101] In the practice of the present invention, liquid lost circulationadditive may be formed by mixing the various components in any form (dryform or liquid or slurry form) in any suitable order utilizing mixingtechniques as know to those in the art. If the various components aremixed in dry form, this dry mixture may subsequently may be contactedwith water or aqueous solution to form a liquid lost circulationadditive.

[0102] Lost circulation fluids are known to those of skill in the art,and in the overwhelming number of cases would generally be of thecategory of well fluid known as drilling fluids, although in fewinstances, lost circulation fluids can be a completion fluid. Generallysuch lost circulation drilling fluids include a solid phase and a liquidphase in which a density agent has been included to increase the densityof the fluid, and of course, lost circulation materials.

[0103] In a method of treating a lost circulation fluid, the lostcirculation fluid to be treated is contacted with a liquid or solid formof the lost circulation additive of the present invention. Preferably,the lost circulation fluid is contacted with a dry mixture (i.e., solidform) of the lost circulation additive.

[0104] A well fluid of the present invention comprises a traditionallost circulation fluid and the lost circulation additive of the presentinvention.

[0105] In a method of operating a well of the present invention in whicha well fluid is circulating down from the surface of the well, throughthe drill string positioned in a wellbore, and out through openings inthe drill bit such that the well fluid is then circulated upwardly inthe annulus between the side of the wellbore and the rotating drillstring, the present invention includes circulating such a well fluidcomprising the lost circulation additive. The lost circulation additivecan be added in liquid or solid form to the circulating fluid.Alternatively, the lost circulation additive may be added to the fluidprior to it being circulated.

[0106] In well operation, it is also known to define a verticallylimited zone into which a slurry is then pumped and subsequentlysqueezed by application of pressure (either from the formation itself,or by application of pressure to the zone). In a method of performing awell operation of the present invention, the lost circulation fluid ofthe present invention is pumped into a desired vertically defined zonein the well, and then “squeezed” to dewater the fluid such that a plugof the filter aid remains behind and the solution of polymer andcrosslinking agent migrates into the formation. The filter aid plugremains in place to prevent or slow down the escape of the solution backinto the well allowing time for the solution to form a gel plug.

EXAMPLES

[0107] The following examples are provided merely to illustrate some butnot all of the embodiments of the present invention, and are notintended to, nor do they, limit the scope of the claims.

[0108] DE

[0109] The DE utilized in this example was that produced by Eagle PicherMinerals, Inc., and sold under the trademark CELATOM® Diatomite ET-905.As measured, the particle size distribution was:

[0110] 8% +200 mesh

[0111] 92% −200 mesh

[0112] Polymer

[0113] The polymers utilized were obtained from Ciba and awater-soluble, crosslinkable, carboxylate-containing acrylamidepolymers, CIBA 254 (MW from 300,000 to less than 500,000) and CIBA 935(MW from 6 to 9 million).

[0114] Crosslinking Agent

[0115] The crosslinking agent was chromium acetate. FormulationsFormulation No. 1 17.5 grams 254   5 grams CrIII Acetate 27.5 grams DEFormulation No. 2   12 grams 254   3 grams CrIII Acetate   25 grams DEFormulation No. 1   5 grams 935   3 grams 254  1.2 grams CrIII Acetate30.8 grams DE

[0116] Filter Press Test

[0117] This test was run to simulate the dewatering of the DE in asubterranean formation, and subsequent formation of a plug of DE andseparate crosslinked polymer.

[0118] 30 ml. of plain tap water was added to a beaker and subjected tomixing at 10,000 rpm in a Hamilton Beach commercial drink mixer with asolid agitator. To this blending water was added the above formulations(three separate runs). The sample was allowed to blend for 5 minutes at10,000 rpm. After the 5 minutes of blending, this mixture was placedinto the cylinder of a filter press in which substantial dewatering ofthe DE slurry occured without any pressure applied. Subsequently, 80 psiof pressure was applied to further dewater and consolidate the DE.Finally, heat was applied to the filter press to heat the consolidatedDE and liquid run off. Both the filter press cylinder and collected runoff (water soluble crosslinkable polymer and crosslinking agent—novisible DE) were placed into a 160 deg. F water bath and allowed tocrosslink. Without being limited in theory, applicant believes thatresidual polymer remaining in the DE after dewatering crosslinks andserves to promote the consolidation of the DE. Once crosslinked, thecollected run off for all of the formulations promotes a rigid ringinggel.

[0119] While the illustrative embodiments of the invention have beendescribed with particularity, it will be understood that various othermodifications will be apparent to and can be readily made by thoseskilled in the art without departing from the spirit and scope of theinvention. Accordingly, it is not intended that the scope of the claimsappended hereto be limited to the examples and descriptions set forthherein but rather that the claims be construed as encompassing all thefeatures of patentable novelty which reside in the present invention,including all features which would be treated as equivalents thereof bythose skilled in the art to which this invention pertains.

I claim:
 1. A lost circulation additive comprising a dry mixture ofwater soluble crosslinkable polymer, a crosslinking agent, and a filteraid.
 2. The additive of claim 1, wherein the filter aid is selected fromthe group consisting of diatomaceous earth, perlite, glass beads,magnesium silicate, solid thermoplastic or thermoset polymers, talc, andcalcium silicate.
 3. The additive of claim 2, wherein the polymer is ana carboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 4. The additive of claim 3, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 5. Theadditive of claim 4, wherein the polymer comprises a low molecularweight polymer having a molecular weight less than 200,000, and a highmolecular weight polymer having a molecular weight of at least 200,000.6. The additive of claim 4, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 7. The additive of claim 6, whereinthe filter aid is diatomaceous earth.
 8. The additive of claim 6,wherein the filter aid is pearlite.
 9. The additive of claim 6, furthercomprising reinforcing material selected from the group consisting ofhydrophilic fibers, hydrophobic fibers, and comminuted plant material.10. A well fluid comprising a lost circulation fluid, water solublecrosslinkable polymer, a crosslinking agent, and a filter aid.
 11. Thewell fluid of claim 10, wherein the filter aid is selected from thegroup consisting of diatomaceous earth, perlite, glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymers, talc, and calciumsilicate.
 12. The well fluid of claim 11, wherein the polymer is an acarboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 13. The well fluid of claim 12, wherein thefilter aid comprises at least one of diatomaceous earth or pearlite. 14.The well fluid of claim 13, wherein the polymer comprises a lowmolecular weight polymer having a molecular weight less than 200,000,and a high molecular weight polymer having a molecular weight of atleast 200,000.
 15. The well fluid of claim 13, wherein the polymer is awater soluble, carboxylate containing acrylamide, and the crosslinkingagent is a chromium (III) carboxylate complex.
 16. The well fluid ofclaim 15, wherein the filter aid is diatomaceous earth.
 17. The wellfluid of claim 15, wherein the filter aid is pearlite.
 18. The wellfluid of claim 15, further comprising reinforcing material selected fromthe group consisting of hydrophilic fibers, hydrophobic fibers, andcomminuted plant material.
 19. A method of modifying a lost circulationfluid comprising: (a) contacting the lost circulation fluid with watersoluble crosslinkable polymer, a crosslinking agent, and a filter aid toform a modified lost circulation fluid.
 20. The method of claim 19,wherein the filter aid is selected from the group consisting ofdiatomaceous earth, perlite, glass beads, magnesium silicate, solidthermoplastic or thermoset polymers, talc, and calcium silicate.
 21. Themethod of claim 20, wherein the polymer is an a carboxylate-containingpolymer, and the crosslinking agent is selected from the groupconsisting of chromium (III) carboxylate complexes, aldehydes,dialdehydes, formaldehydes, glutaraldehyde, dichromates, titaniumchelates, phenols, substituted phenols, ethers, aluminum citrate, andaluminates.
 22. The method of claim 21, wherein the filter aid comprisesat least one of diatomaceous earth or pearlite.
 23. The method of claim22, wherein the polymer comprises a low molecular weight polymer havinga molecular weight less than 200,000, and a high molecular weightpolymer having a molecular weight of at least 200,000.
 24. The method ofclaim 22, wherein the polymer is a water soluble, carboxylate containingacrylamide, and the crosslinking agent is a chromium (III) carboxylatecomplex.
 25. The method of claim 24, wherein the filter aid isdiatomaceous earth.
 26. The method of claim 24, wherein the filter aidis pearlite.
 27. The method of claim 19, wherein water solublecrosslinkable polymer, a crosslinking agent, and a filter aid.
 28. Amethod for decreasing fluid loss from a borehole into a subterraneanformation comprising: (a) providing a lost circulation fluid comprisingwater or an aqueous solution, water soluble crosslinkable polymer, acrosslinking agent, and a filter aid; (b) injecting the lost circulationfluid into the wellbore; and (c) dewatering the lost circulation fluidto force the polymer and crosslinking agent into the formation, and toform the filter aid into a plug.
 29. The method of claim 28, wherein thefilter aid is selected from the group consisting of diatomaceous earth,perlite, glass beads, magnesium silicate, solid thermoplastic orthermoset polymers, talc, and calcium silicate.
 30. The method of claim29, wherein the polymer is an a carboxylate-containing polymer, and thecrosslinking agent is selected from the group consisting of chromium(III) carboxylate complexes, aldehydes, dialdehydes, formaldehydes,glutaraldehyde, dichromates, titanium chelates, phenols, substitutedphenols, ethers, aluminum citrate, and aluminates.
 31. The method ofclaim 30, wherein the filter aid comprises at least one of diatomaceousearth or pearlite.
 32. The method of claim 31, wherein the polymercomprises a low molecular weight polymer having a molecular weight lessthan 200,000, and a high molecular weight polymer having a molecularweight of at least 200,000.
 33. The method of claim 31, wherein thepolymer is a water soluble, carboxylate containing acrylamide, and thecrosslinking agent is a chromium (III) carboxylate complex.
 34. Themethod of claim 33, wherein the filter aid is diatomaceous earth. 35.The method of claim 33, wherein the filter aid is pearlite.
 36. Themethod of claim 33, further comprising reinforcing material selectedfrom the group consisting of hydrophilic fibers, hydrophobic fibers, andcomminuted plant material.
 37. A method for decreasing fluid loss from aborehole into a subterranean formation comprising: (a) providing a lostcirculation fluid comprising water or an aqueous solution, water solublecrosslinkable polymer, a crosslinking agent, and a filter aid; (b)injecting the lost circulation fluid into the formation and into theopening to be plugged; and (c) applying pressure to dewater the lostcirculation fluid to force the polymer and crosslinking agent into theformation, and to form the filter aid into a plug.
 38. The method ofclaim 37, wherein the filter aid is selected from the group consistingof diatomaceous earth, perlite, glass beads, magnesium silicate, solidthermoplastic or thermoset polymers, talc, and calcium silicate.
 39. Themethod of claim 38, wherein the polymer is an a carboxylate-containingpolymer, and the crosslinking agent is selected from the groupconsisting of chromium (III) carboxylate complexes, aldehydes,dialdehydes, formaldehydes, glutaraldehyde, dichromates, titaniumchelates, phenols, substituted phenols, ethers, aluminum citrate, andaluminates.
 40. The method of claim 39, wherein the filter aid comprisesat least one of diatomaceous earth or pearlite.
 41. The method of claim40, wherein the polymer comprises a low molecular weight polymer havinga molecular weight less than 200,000, and a high molecular weightpolymer having a molecular weight of at least 200,000.
 42. The method ofclaim 40, wherein the polymer is a water soluble, carboxylate containingacrylamide, and the crosslinking agent is a chromium (III) carboxylatecomplex.
 43. The method of claim 42, wherein the filter aid isdiatomaceous earth.
 44. The method of claim 42, wherein the filter aidis pearlite.
 45. The method of claim 42, further comprising reinforcingmaterial selected from the group consisting of hydrophilic fibers,hydrophobic fibers, and comminuted plant material.
 46. A method ofcirculating a lost circulation fluid in a welbore penetrating asubterranean formation, comprising: (a) providing a lost circulationfluid comprising water or an aqueous solution, water solublecrosslinkable polymer, a crosslinking agent, and a filter aid; (b)circulating the lost circulation fluid in the wellbore.
 47. The methodof claim 46, wherein the filter aid is selected from the groupconsisting of diatomaceous earth, perlite, glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymer beads, talc, andcalcium silicate.
 48. The method of claim 47, wherein the polymer is ana carboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 49. The method of claim 48, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 50. Themethod of claim 49, wherein the polymer comprises a low molecular weightpolymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000.51. The method of claim 49, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 52. The method of claim 51, whereinthe filter aid is diatomaceous earth.
 53. The method of claim 51,wherein the filter aid is pearlite.
 54. The method of claim 51, furthercomprising reinforcing material selected from the group consisting ofhydrophilic fibers, hydrophobic fibers, and comminuted plant material.55. A method of modifying a lost circulation fluid circulating in awellbore penetrating a subterranean formation, comprising: (a)introducing a water soluble crosslinkable polymer, crosslinking agent,and filter aid to the circulating lost circulation fluid.
 56. The methodof claim 55, wherein the filter aid is selected from the groupconsisting of diatomaceous earth, perlite, glass beads, magnesiumsilicate, solid thermoplastic or thermoset polymer beads, talc, andcalcium silicate.
 57. The method of claim 56, wherein the polymer is ana carboxylate-containing polymer, and the crosslinking agent is selectedfrom the group consisting of chromium (III) carboxylate complexes,aldehydes, dialdehydes, formaldehydes, glutaraldehyde, dichromates,titanium chelates, phenols, substituted phenols, ethers, aluminumcitrate, and aluminates.
 58. The method of claim 57, wherein the filteraid comprises at least one of diatomaceous earth or pearlite.
 59. Themethod of claim 58, wherein the polymer comprises a low molecular weightpolymer having a molecular weight less than 500,000, and a highmolecular weight polymer having a molecular weight of at least 500,000.60. The method of claim 58, wherein the polymer is a water soluble,carboxylate containing acrylamide, and the crosslinking agent is achromium (III) carboxylate complex.
 61. The method of claim 60, whereinthe filter aid is diatomaceous earth.
 62. The method of claim 60,wherein the filter aid is pearlite.
 63. The method of claim 55, whereinthe water soluble crosslinkable polymer, crosslinking agent, and filteraid, are all in solid form.